Heat exchanger array system and method for an air thermal conditioner

ABSTRACT

An air thermal conditioning system, for at least one of heating air and cooling air, which includes a cross-flow heat exchanger array. The cross-flow heat exchanger array includes a plurality of planar membrane heat exchangers disposed in parallel with a space separating adjacent planar membrane heat exchangers. Each of the planar membrane heat exchangers include a first sheet; a second sheet coupled to the first sheet; and at least one fluid chamber defined by the first and second sheets, with the at least one fluid chamber extending between first and second ends of the planar membrane heat exchangers and opening to a first and second port at the first and second ends respectively.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/161,029 filed May 20, 2016, which is non-provisional of and claimspriority to U.S. Provisional Application No. 62/164,443, filed May 20,2015, entitled “Membrane Heat Exchanger System and Method” whichapplication is hereby incorporated herein by reference in its entiretyand for all purposes. This application is also related to U.S.application Ser. No. 15/161,064 filed May 20, 2016 having attorneydocket number 105198-007US1 entitled “Near-isothermalcompressor/expander.”

BACKGROUND

In various embodiments, the temperature difference AT across a heatexchanger directly equates to a loss in exergy. The Carnot coefficientsof performance for heat pumps in cooling and heating systems are:

$\begin{matrix}{{COP}_{cooling} = {{\frac{T_{c} - {\Delta\; T}}{\left( {T_{h} + {\Delta\; T}} \right) - \left( {T_{c} - {\Delta\; T}} \right)}\mspace{14mu}{COP}_{heating}} = \frac{T_{h} + {\Delta\; T}}{\left( {T_{h} + {\Delta\; T}} \right) - \left( {T_{c} - {\Delta\; T}} \right)}}} & (1)\end{matrix}$

where T_(h) and T_(c) are hot and cold temperatures at either end of thesystem and ΔT is the additional temperature difference required totransfer heat to the air through a heat exchanger. However, ΔT isconstrained by the need to exchange heat at a sufficient rate; this heatflux from one fluid, through a wall, into a second fluid is a functionof the combined heat transfer due to convection in both fluids andconduction and is given by

$\begin{matrix}{Q = {{h_{1}A\;\Delta\; T_{1}\mspace{14mu} Q} = {{h_{2}A\;\Delta\; T_{2}\mspace{14mu} Q} = {\left. \frac{{kA}\;\Delta\; T_{3}}{t}\Rightarrow Q \right. = \frac{A\;\Delta\; T}{\frac{1}{h_{1}} + \frac{1}{h_{2}} + \frac{t}{k}}}}}} & (3)\end{matrix}$

where A is the surface area of the heat exchanger, t is the wallthickness, k is the thermal conductivity of the material, h₁ and h₂ arethe heat transfer coefficients of either fluid, and Q is the heattransfer.

Power plants and other implementations are similarly limited by heatexchanger ΔT via the Carnot efficiency

$\begin{matrix}{\eta = \frac{T_{h} - \left( {T_{c} + {\Delta\; T}} \right)}{T_{h}}} & (3)\end{matrix}$

In various embodiments, laminar flow heat transfer and flow losses areapproximated by

$\begin{matrix}{Q = {{\frac{{Nu}\mspace{14mu}{kA}\;\Delta\; T}{d}\mspace{14mu} P_{fan}} = \frac{8A\;\mu\; v^{2}}{d}}} & (4)\end{matrix}$

where N_(u) is the Nusselt number, d is the effective tube diameter,P_(fan) is the required fan power, μ is the viscosity, and v is thefluid velocity.

The heat transfer rate in a heat exchanger can be directly proportionalto the surface area in the heat exchanger. Increasing the surface areacan increase the overall heat transfer, thereby increasing performance.This can be impractical with conventional heavy metallic heatexchangers. Additionally, conventional metallic heat exchangers becomefragile and corrosion sensitive at small thickness.

Metallic fin-and-tube heat exchangers, similar to automotive radiators,are the current standard for conventional heat exchangers. Most metalshave high densities and become fragile and corrosion sensitive at thinfilm thicknesses. Thus, metallic heat exchangers are heavier and moreexpensive than otherwise required for a given operating pressure ordesired heat transfer rate, and typically rely on high-power fans whichreduce efficiency.

In view of the foregoing, a need exists for improved membrane heatexchanger systems and methods in an effort to overcome theaforementioned obstacles and deficiencies of conventional systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a, 1 b, 2 a and 2 b are example perspective drawingsillustrating various embodiments of a membrane heat exchanger.

FIGS. 3a and 3b illustrate a further embodiment of a membrane heatexchanger in a flat configuration and FIG. 3c illustrates the membraneheat exchanger of FIGS. 3a and 3b in an expanded configuration.

FIGS. 4a and 4b illustrate a further embodiment of a membrane heatexchanger in a flat configuration and FIG. 4c illustrates the membraneheat exchanger of FIGS. 4a and 4b in an expanded configuration.

FIGS. 5a and 5b illustrate yet another embodiment of a membrane heatexchanger.

FIGS. 6a and 6b illustrate still further embodiments of a membrane heatexchanger.

FIG. 7a illustrates an example embodiment of a printer configured forroll-to-roll printing of fluidic chambers.

FIG. 7b illustrates an embodiment of a full roll laser welder.

FIG. 7c illustrates an embodiment of a processing unit and finalassembly table.

FIGS. 8a and 8b illustrate a welding apparatus in accordance with oneembodiment that includes a welding head that is configured to weld seamsin an adjoining pair of sheets.

FIG. 9 illustrates a plurality of membrane heat exchangers configuredtogether into a cross-flow heat exchanger array.

FIG. 10 illustrates a further embodiment of a heat exchanger array thatcomprises a plurality of stacked membrane heat exchangers that aresupported within a housing.

FIG. 11 illustrates a first embodiment of a heat exchanger assemblyhaving a plurality of heat exchanger arrays disposed in a separated andstacked configuration.

FIG. 12 illustrates an example of a heat exchanger system that comprisesa plurality of heat exchanger arrays and comprises a fan assembly.

FIG. 13 illustrates another example of a heat exchanger assembly thatcomprises a plurality of membrane heat exchangers disposed in acylindrical configuration about a fan assembly to define a flow cavity.

FIG. 14 illustrates a further example of a heat exchanger assembly thatcomprises a plurality of stacked membrane heat exchangers disposed abouta fan assembly to define a flow cavity.

FIG. 15 illustrates a bottom view of the heat exchanger assembly of FIG.14.

FIG. 16 illustrates a further embodiment of a membrane heat exchangerthat can form a portion of a heat exchanger assembly.

FIG. 17 illustrates a further embodiment of a membrane heat exchangerthat comprises a circular housing that surrounds a fan assembly anddefines a flow cavity.

FIGS. 18a, 18b, 19a, 19b and 20 illustrate various embodiments ofmembrane heat exchanger systems.

FIG. 21 illustrates an example heat exchanger that can be deployed in adesalination system.

FIG. 22 illustrates an example embodiment of a mechanical vaporcompression desalination system.

FIG. 23 illustrates an example embodiment of a multi-stage thermaldesalination system that comprises a pressure vessel body that defines aplurality of pressure chambers arranged in series with each stage at aslightly lower pressure and temperature than the previous stage.

FIG. 24 illustrates an example embodiment of isothermal compressor thatcomprises a cylinder which defines a compression cavity.

FIGS. 25a, 25b and 25c illustrate chambers that comprise fluid such as agas that can be squashed flat when the membrane heat exchanger iscompressed.

FIG. 26 illustrates a further embodiment of a compressible membrane heatexchanger, which is shown having a coiled planar body that defines achamber that extends between a first and second end.

FIG. 27 illustrates an isothermal compressor that comprises a tank bodydefining a compression chamber into which a fluid (e.g., oil, water, orthe like) can be pumped to compress a membrane heat exchanger disposedwithin the compression chamber.

FIG. 28 illustrates an isothermal engine that comprises a first andsecond bellows that define a respective compression chamber having amembrane heat exchanger disposed therein.

FIG. 29 illustrates an example embodiment of an isothermal engine havingthe bellows disposed in a parallel arrangement instead of in a 90°arrangement as in FIG. 28.

FIG. 30 illustrates an isothermal engine having non-compressiblecylinders in which respective membrane heat exchangers are disposed.

FIG. 31 illustrates an array of elongated shielding channels that arenormal to the surface of a radiator or membrane heat exchanger and arereflective, effectively acting as a short distance light-pipe forpassing radiation to space.

It should be noted that the figures are not drawn to scale and thatelements of similar structures or functions are generally represented bylike reference numerals for illustrative purposes throughout thefigures. It also should be noted that the figures are only intended tofacilitate the description of the preferred embodiments. The figures donot illustrate every aspect of the described embodiments and do notlimit the scope of the present disclosure.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning to FIG. 1 a, a first embodiment 100A of a membrane heatexchanger 100 is shown as comprising a body 105 that includes anelongated chamber 110 disposed within a sheet portion 115, with thechamber 110 extending from both sides of the body 105. The chamber 110includes a pair of ends 111 with a snaking or switchback portion 112 anda wrapping portion 113 that surrounds the switchback portion 112 suchthat the ends 111 are disposed proximate to each other. FIG. 1billustrates an alternative configuration 100B wherein a trio of thestructures 100A of FIG. 1a are disposed in a stacked arrangement.

FIG. 2a illustrates a further embodiment 100C of a membrane heatexchanger 100 that is similar to the embodiment of FIG. 1 a, but withoutthe wrapping portion 113. Accordingly, the ends 111 of the chamber 110are disposed on opposing ends of the switchback portion 112. FIG. 2billustrates a further example embodiment 110C, wherein the elongatedportions of the switchback portion 112 are not linear as shown in FIGS.1 a, 1 b and 2 b and instead define a wave configuration.

As discussed in more detail herein, some embodiments of a membrane heatexchanger 100 can be defined by first and second thin-film polymermembrane sheets that are stacked and coupled together to define achamber 110 having at least a first and second end 111. For example,FIGS. 3a-c and 4a-c illustrate two example embodiments 100E, 110F ofsuch a membrane heat exchanger 100.

Turning to FIGS. 3a and 3b , top and perspective views of the membraneheat exchanger 100E are illustrated in a flat configuration, with thechamber 110 being defined at least by a seam 301, which joins a pair ofsheets 115. The planar portions of the membrane heat exchanger 100between the chamber 110 can be defined by a planar coupling 302 betweena pair of sheets 115. FIG. 3c illustrates an example of the membraneheat exchanger 100E in an expanded configuration, wherein the chamber110 is expanded by fluid filling the chamber 110. In this example, thesheet(s) 115 are shown deforming due to the chamber 110 being filledwith fluid.

FIGS. 4a-c illustrate a further example embodiment 110F of a membraneheat exchanger 100 that can be defined by a pair of sheets 115, coupledtogether by a planar coupling 302 and/or seam 301. In this example, thechamber 110 rectangularly coils from a peripheral portion of themembrane heat exchanger 100E to a central portion of the membrane heatexchanger 100 with the ends 111 of the chamber 110 being respectivelydisposed at the peripheral and central portions.

Although specific embodiments of membrane heat exchangers 100 andchambers 110 are discussed above, further embodiments can have chambers110 of any suitable size, shape and configuration and the presentexamples should not be construed to be limiting on the wide variety ofconfigurations of membrane heat exchangers 100 that are within the scopeand spirit of the present disclosure. For example, FIGS. 5a and 5billustrate an example of a pillow-plate heat exchanger 100G inaccordance with an embodiment, which includes a planar body 105 thatcomprises a chamber 110 defined at least in part by a plurality ofdimples 510 and a bifurcating seam 520 that couples opposing sheets 115.

Additionally, while various embodiments described herein illustrate amembrane heat exchanger 100 having a heat exchanger body 105 thatdefines a single chamber 110 with a pair of ends 111; in furtherembodiments, a heat exchanger body 105 can define a plurality ofchambers 110. For example, FIGS. 6a and 6b illustrate exampleembodiments 100H, 100I of a membrane heat exchanger 100 that comprisesfive and nine chambers 110 respectively. In these example embodiments100H, 100I a plurality of nested chambers 110 are illustrated in aswitchback configuration 112 with respective ends 111 of the chambers110 terminating at respective ports 650 disposed on opposing corners ofthe heat exchanger body 105. As discussed herein, the chambers 110 canbe defined by seams 301 and/or planar coupling portions 302 that couplea pair of opposing sheets 115.

Accordingly, various embodiments of a membrane heat exchanger 100 cancomprise of a plurality of small and thin-walled chambers 110 instead ofheavy, metal tubes with soldered-on fins as in conventional heatexchanger systems. Thus, various embodiments of a membrane heatexchanger can be configured to decrease AT while keeping Q constant byincreasing the surface area A, which can be achieved (without increasesto mass and cost) by a small thickness t.

By Equation 2, low thermal conductivity materials can be used in someembodiments of heat exchangers 100 by using a small thickness t. Basedon hoop stress, the wall thickness required to hold a given pressure canbe:

t=(Pressure·Tube radius)/Material stress   (5)

In various embodiments, chambers 110 of a small radius can generatelighter and cheaper membrane heat exchanger 100 with better thermalconduction compared to conventional heat exchangers. For example, invarious embodiments, four times as many chambers 110 of half thediameter doubles heat transfer for the same system mass/cost. Diametersof chambers 110 in the 1-10 mm range can be provided in accordance withsome embodiments, with surface heat transfer coefficients h of around50-100 W/(m²K) for air, and 5,000-10,000 W/(m²K) for flowing water andthe condensing and evaporating of water.

Membrane heat exchangers 100 can comprise various suitable materials,including polymers, and the like. In one preferred embodiment,Polyethylene terephthalate (PET) films can be used, which in someimplementations can have strengths as high as 200 MPa or more andthermal conductivities k in the 0.15-0.4 W/(mK) range, depending onadditives. From Equation 5, in some embodiments, a desired wallthickness is t=0.005 mm for a safe working stress of 30 MPa, tubediameter of 3 mm, and an operating pressure of 0.1 MPa (oneatmosphere)(other suitable thicknesses can be employed in furtherembodiments). Thus k/t 30,000-80,000 W/(m²K), is higher than the abovesurface heat transfer coefficients h, so by Equation 2 the relativelylow thermal conductivity of a thin PET film is not a limiting factor forperformance in various embodiments.

Accordingly, embodiments that employ thin film polymer membranes canenable a substantial increase in surface area and heat exchangerperformance. In other words, while polymers can have lower thermalconductivities k than metal, their thickness can be made small enoughthat t/k is small relative to 1/h₁ and 1/h₂.

As discussed herein, the heat transfer rate in a membrane heat exchanger100 can be directly proportional to the surface area of the membraneheat exchanger 100. Accordingly, increasing the surface area canincrease the overall heat transfer, thereby increasing performance. Invarious embodiments, computer-controlled manufacturing and polymerprocessing can enable the fabrication of membrane heat exchanger 100with thin walls and small masses, enabling increased surface areas whilemaintaining effectiveness of the membrane heat exchanger 100.

Accordingly, various embodiments discussed herein can use thin polymericmembranes for high surface-area membrane heat exchangers 100, loadedwithin appropriate safety factors of the hoop-stress limit. In someembodiments, such a configuration can be enabled via patterned chambers110 which can be generated via laser processing of pairs of sheets asdiscussed herein.

Using computer-controlled manufacturing tools, a number of fabricationoptions available with thin polymeric membranes, which can be amenableto rapid-prototyping as well as production. Additionally, the resilienceof polymeric materials enables their use in various embodiments evenwhen processed into very thin films—i.e., films thin enough to havenegligible impact on the heat transfer rate across them.

For example, the heat transfer rate, Q, across a heat exchanger can beshown to be:

$\begin{matrix}{Q = {{h_{0}A\;\Delta\; T_{LM}} = \frac{A\;\Delta\; T_{LM}}{\frac{1}{h_{w}} + \frac{1}{h_{a}} + \frac{t}{k_{m}}}}} & (1)\end{matrix}$

where h₀ is the overall heat transfer coefficient, A is the surface areaof the heat exchanger, ΔT_(LM) is the logarithmic mean temperaturedifference across the heat exchanger, h_(w) is the heat transfercoefficient of the hot-fluid that is being cooled, h_(a) is the heattransfer coefficient of the cooling air, k_(m) is the thermalconductivity of the membrane barrier wall between the two fluids, and tis the thickness of that barrier.

In some embodiments, increasing the overall heat transfer in a membraneheat exchanger 100 can be brought about by increasing the surface areaof the membrane heat exchanger 100 and/or increasing the overall heattransfer coefficient. In an air-cooled heat membrane heat exchanger 100the overall heat transfer coefficient can be dominated by the heattransfer coefficient of the air and there is little opportunity toincrease the value of h₀. However, the low density and thin walls of amembrane heat exchanger 100 can allow the surface area to be greatlyincreased which can improve performance.

Numerically, h_(w)>>h_(a), so for a membrane heat exchanger 100 withliquid on one side and air on the other, the 1/h_(w) term is very smallcompared to 1/h_(a). Metals typically have good thermal conductivity(around 10-400 W/mK), so in conventional heat exchangers the t/k_(m)term can also be ignored compared to 1/h_(a). For many polymers, thermalconductivity may be smaller, (e.g., 0.1-0.4 W/mK) but by providing abarrier less than 1 mm thick, the t/k_(m) term is still small comparedto 1/h_(a), meaning that the polymer wall will not significantly impedeheat transfer through the heat exchanger compared to a metal wall.Therefore, for a given desired rate of heat transfer, ΔT can bedecreased in some embodiments, provided that the surface area can beproportionally increased.

While low thermal conductivity materials can be used in heat membraneheat exchangers 100 if their thickness is very low, the wall thicknesscan specified by the requirement to withstand the pressure forcing fluidthrough the chamber(s) 110 of the membrane heat exchanger 100. Based onhoop stress, the wall thickness required to hold a given pressure is:

$\begin{matrix}{t = \frac{pr}{\sigma}} & (2)\end{matrix}$

where p is the pressure in the tube, r is the radius of the tube, and σis the operating stress.

If we assume an example polymer film thickness of 0.1 mm (4 mil),high-density polyethylene (HDPE) with a maximum stress of 25 MPa and aworking stress of 5 MPa, a 4 mm diameter tube can have a burst pressureof 1.25 MPa (180psi), and a working pressure of 0.25 MPa (36 psi). Givena high-density polyethylene HDPE density of 970 kg/m³ this polymer filmwould have a mass of 0.097 kg/m². In further embodiments, higherstrength polymers can be used and/or tube diameters can be reduced. Thisindicates that such embodiments of membrane heat exchangers 100 can bemechanically resilient in addition to thermally responsive.

For the air side of the heat exchanger, the heat transfer rate, Q, canconstrain the air mass flow rate, m,

Q=mc _(p)ΔT_(a)   (3)

where c_(p) is the specific heat capacity of air, and ΔT_(a) is thedifference in temperature between the air entering and exiting the heatexchanger. Increasing mass flow across the heat exchanger surface can beaccomplished through increased air velocity, but that brings with itincreased power consumption, which may not be desirable. Assuminglaminar flow, the fans power consumption depends on the square of thelinear velocity of the air,

P=(8Aμv ²)/d   (4)

where v is the air velocity through the heat exchanger, d is theeffective diameter of the air flow passage, μ is the viscosity of thefluid, and A is the surface area of the heat exchanger. Increasing theheat exchanger area can increase the flow resistance and thus the fanpower for a given velocity, however the air velocity can be reduced byincreasing the cross-sectional area accepting the airflow. Since fanpower can be proportional to the cross sectional area but also to thesquare of velocity, the trade-off of increased area for decreasedvelocity can result in a net reduction in fan power.

At small or large scale, embodiments of membrane heat exchangers 100 canbe made using manufacturing techniques and by optimization of thegeometric design, fluid connections, and pumping controls. By moving tosmall diameter chambers 110 and thin materials, a large number ofparallel linear flow paths can be enabled in various embodiments (e.g.,as illustrated in FIGS. 6a and 6b ). In one example manufacturingprocess, a computer-controlled laser welding process can be used togenerate arrays of chambers 110 from the controlled welding of twoplastic sheets.

Accordingly, various embodiments comprise the use of thin polymers formembrane heat exchanger construction and the manufacture of suchmembrane heat exchangers 100 using computer-controlled plastic weldingsystem. The use of a plurality of narrow chambers 110 made from thinpolymer films in some embodiments can create a barrier between heatedwater and cooling air that is thin enough such that the thermallynon-conductive polymer only minimally impacts the overall heat transfercoefficient. Combined with research in computer-controlled laserwelding, these membrane heat exchangers 100 can be rapidly prototypedand provide for volume production, as well. The use of low cost, lowweight polymers and high-throughput manufacturing enables embodiments ofthe membrane heat exchangers 100 to have larger heat exchange areas forless cost, leading to favorable coefficients of performance.

Various embodiments can comprise computational, physics-basedoptimization tools for polymeric heat exchanger design. For example,some embodiments include software tools for membrane heat exchanger 100design optimization.

Further embodiments include a laser processing manufacturing method thatenables high geometric and three-dimensional complexity fromtwo-dimensional patterns produced rapidly and cost effectively. Someembodiments can provide for large area and continuous fabrication. Stillfurther embodiments can include 20-year heat exchanger lifetimes for theselected materials.

Some embodiments comprise computer-controlled fabrication methods forwelding and cutting polymer films into intricate fluidic networks andstructures, for rapid prototyping and commercial production. Furtherembodiments comprise computational modeling and optimization of fluidicnetworks and membrane patterns to minimize flow restrictions andmaximize thermal transfer.

TABLE 1 Specification of an example 20 kW system. Parameter CalculatedRequired Heat transfer rate Q 23.6 kW 20 kW Pump power 18.1 W Fan power39.0 W Total pump and fan power 57.1 W COP 350.6 >200 Effectiveness ε.65   >.6 Overall heat transfer CoE 66. W/m²K Surface area 33. m²

Still further embodiments leverage materials science and chemistry ofpolymer thin films, working with resin and additive manufacturers, todevelop materials with optimized thermal properties, long functionallifetimes, controlled surface chemistry, and robust processability.Accordingly, various embodiments can comprise computationally enabledheat exchanger design and optimization, selection of robust materialsamenable to inexpensive and ultimately high-throughput fabrication, andcareful performance and lifetime testing and characterization. Forexample, computational modeling and optimization can be used to designcooling fluidic networks that optimize air and coolant flow geometriesfor maximal thermal transfer and increased system efficiency.

Creation of three-dimensional networks of chambers 110 from sheets oftwo-dimensional film can be modeled and simulated, including simulatingthe filling or inflation of these networks to get net three-dimensionalgeometry. Such two-dimensional models can be physically produced vialaser film processing utilizing a roll feed CNC laser cutter and welderas discussed in further detail herein (see e.g., FIGS. 20a-c and FIGS.21a-b ). Some embodiments can comprise surface chemistry modificationsto improve weld, lamination, or the like. Additives can be selected forimproved material processing, heat exchanger performance, and the like.

In some embodiments, membrane heat exchangers 100 can comprise a thinmetallic foil. Such metal membrane heat exchangers 100 can beconstructed/welded in a similar manner to the polymer heat exchangersdiscussed herein. Metal heat exchangers can be advantageous forautomatable construction and higher temperature operation.

For determining the design of membrane cooling networks or chambers 110,in some embodiments, a parametric geometry authoring environment can beused, incorporating simulation of the fundamental requirements of thesystem—necessary pumping and fan power, heat transfer performance,material cost, and the like. While these (and other relevant parameterssuch as total internal volume, total bounding volume, etc.) can bedynamic “in the loop” calculations from a given geometry which theauthor can use as a metric for analysis, they can also be specified asdesign inputs, and an integrated constrained optimization can suggestgeometries and properties which optimally satisfy theapplication-specific efficiency and cost targets.

The underlying coolant flow model for this simulation and optimizationlayer can incorporate laminar and/or turbulent incompressible flow. Onthe liquid side, the pumping power and the convective heat transfercoefficient can be determined by employing equations of internal,incompressible flow, for both the laminar and turbulent cases, where, inthe turbulent case, empirical relations can be used for friction factorin determining head loss. Computational fluid dynamics (CFD) topologyoptimization methods and genetic algorithms can be built on top of thismodel to produce optimal tube geometries.

One model of the forced-air side of the boundary can be used forinforming high-level geometry and flow configuration decisions withreasonably low latency. In some embodiments, in can be beneficial tohave a more sophisticated high-resolution model for specific concerns,such as fine-tuning optimal spacing between the coolant tubes andlayouts for efficient airflow. Such a model may more accurately quantifylocal liminal heat transfer coefficients, particularly when the airflowis perpendicular or at various angles to the coolant tubes, as well asaccount for the possibility of non-negligible hydrodynamic and thermalentry lengths. Such a model can be run offline, and may not be used atthe integrated optimization stage in some embodiments, and as such couldbe chosen from a range of professional-grade commercially availablecomputational fluid dynamics software.

As illustrated in FIGS. 3c and 4c , filling a membrane heat exchanger100 can change the shape of the body 105 by including the introductionof local buckling and bending. In various embodiments, such geometriccontortions may need to be accounted for and compensated for in thedesign of the membrane heat exchanger 100. Such software can model netshape membrane structures under filling and environmental loading, andcan further include more sophisticated analysis tools, visualization,and coupling of simulation to real-world performance.

Example software for solving the net shape geometry problem ofconstructing and engineering a machine from flexible sheets can includesimulation of an unloaded membrane heat exchanger 100 and a simulatednet shape of the membrane heat exchanger 100. The shrinking along thelong axis caused by filling the tubes with a virtual fluid is apparentas is the buckling of the sheets along the edges as shown in FIGS. 3cand 4c . This modeling can help in the optimization of the design.

Additionally, some embodiments of modeling software can comprise“inverse” inflation simulation. For example, such modeling takes asinput a target 3D shape, given either by the designer or by anoptimization pass, and produces the rest shape to be manufactured, whichfor given materials and subject to specified forces, will as closely aspossible approximate the target under load.

Membrane or sheet joining methods can comprise mechanical methods,adhesive methods, welding methods, and the like. Mechanical methods suchas sewing or clamping/interlocking with rigid parts can be desirable insome embodiments because they can be tolerant processes that are stableacross a variety of process parameters. Adhesive bonding can accommodatea wide variety of material combinations and can be carried out at lowtemperatures in some embodiments.

FIGS. 1 a, 1 b, 2 a, 2 b, 3 a-c, 4 a-c, 5 a and 5 b illustrate variousembodiments of membrane heat exchangers 100, but should not be construedto limit the wide variety of alternative and/or additional shapes,sizes, and structures that are within the scope and spirit of thepresent disclosure. For example, complicated inflatable geometries canbe added to the membrane heat exchanger elements so as to providestructural spacing between adjacent elements. In some embodiments,bubbles can be created within the membrane elements that periodicallyconnect with adjacent heat exchanger elements so as to maintain a givenair gap between heat exchanger elements. In some embodiments, aninflated structure of the heat exchanger elements can be used to addstiffness to the heat exchanger elements and thereby reduce the need forexternal structural support.

Membrane heat exchangers 100 can be fabricated in various suitable ways.For example, FIG. 7a illustrates an example embodiment of a printer 700configured for roll-to-roll “printing” of fluidic chambers 110 andsurface features on an adjoining pair of sheets 710, with the fluidicchambers 110 being at least defined by printed seams 301 as discussedherein. FIG. 7b illustrates an embodiment of a full roll laser welder701 and FIG. 7c illustrates an embodiment of a processing unit and finalassembly table 702.

Coupling of sheets 115 to generate seams 301 and/or planar coupledportions 302 of a membrane heat exchanger 100 can be done in varioussuitable ways as discussed herein including welding. FIGS. 8a and 8billustrate a welding apparatus 800 in accordance with one embodimentthat includes a welding head 805 this is configured to weld seams 301 inan adjoining pair of sheets 710, which are rolled over a welding table810. As illustrated in FIG. 8b , a first and second sheet 116A, 116B canbe disposed on the welding table 810 with a gap 117 therebetween. Thefirst and second sheet 116A, 116B can be pressed together via apressurized stream of gas 806 from the welding head 805 and a laser 807can weld the first and second sheet 116A, 116B at a seam 301 and/orplanar 302 coupling joint. For example, in plastic welding, twothermoplastic material interfaces 116A, 116B can be brought into directcontact and heated above their melting temperature via the laser 807.Compatible materials can then interlock at a molecular level resultingin a continuous matrix of polymer chains, which generates a seam 301and/or planar 302 coupling joint.

One challenge in some welding applications is transferring heat to thejoint interface at the weld location without degrading the integrity ofthe surrounding material. For thick-sectioned parts where it can bedifficult to transfer heat from the outside accessible surface of thepart stack, various suitable methods can be used to generate a weld. Forexample, one method, called hot plate welding, comprises heating thejoint surfaces with the parts separated and then bringing the parts incontact while the joint surfaces remain above the material melttemperature.

Ultrasonic and radio frequency (RF) welding can be used in someembodiments and can comprise transferring vibrations to the jointinterface through the accessible outside parts surfaces and directingthese vibrations to targeted areas where the weld is required using whatare known as energy directors.

Transmissive laser welding can also be used in some embodiments. Forexample, the energy in a laser beam can be turned into heat when itinteracts with a material that is opaque to the wavelength being used.In order to target the heat generated to material interface, in variousembodiments, one of the parts must be transparent to the laserwavelength such that the laser beam passes through it and generates heatat the joint interface when it hits the second, opaque material.

Inductive welding can also be used in some embodiments, where aninterposing material that heats up in presence of an electromagneticfield is placed at the bond interface and then activated with such afield.

A hot air jet can also be used for welding sheets together in variousembodiments. Such a method can serve to both heat and press themembranes together. In various embodiments, the weld-affected zone canfurther be managed by use of cold air jets. Alternatively and/or inaddition, hot fluid jets can be used for welding. With close activesurface following, it is possible to get high effective clampingpressures in a similar manner to a static air or hydraulic bearing.

In further embodiments, membrane heat exchanger elements can bethermal/ultrasonic/radio frequency welded and blanked in one process viaa stamping type operation with a single tool of the desired shape. Thiscan enable high speed and low cost manufacture of heat exchangerelements.

For welding a pair of sheets 116A, 16B, the volume 117 or gap betweenthe sheets 116A, 16B can be actively evacuated, providing a clampingforce, which can be atmospheric pressure or the like. For large surfacearea membrane heat exchangers 100, cumulative weld length can be high insome embodiments. Accordingly, some embodiments can employ redundantwelds, that is, multiple welds side by side, to reduce sensitivity toindividual weld defects.

Various suitable welding techniques can be used, in more elaborateforms, to assemble multiple polymer film heat exchanger elementstogether with integral plumbing pathways. Fluid inlet and outletfittings and hoses, and the like, can be similarly attached to theassembled heat exchanger elements via suitable welding or couplingmethods.

In some embodiments, thin film plastic welding shares many of the samechallenges as thick section plastic welding but can have one or moremitigating factors by nature of the thin section geometry. While it canbe unfeasible to have direct heat transfer to the accessible surface ofa thick section part in some embodiments, in thin film welding, thethickness of the material can be such that this is possible because thethrough-thickness size of the heat affected zone of the weld is similarto that of the whole material.

This fact enables further suitable methods to be used in someembodiments, including direct thermal welding and direct laser welding.In direct thermal welding, two compatible films can be clamped between ahot tool and anvil such that heat is transferred to the joint, meltingthe interface and creating a bond. In direct laser welding a laser beamcan strike two compatible materials and heat the whole joint thickness.

One example implementation includes a direct laser welding process.Here, two layers of LDPE film can be welded together using a CO₂ laserbeam. This process was prototyped using a multi-purpose CNC lasercutter. The laser beam was defocused such that a weld of desired width(˜1-2 mm) was created between the two film layers. A reflective aluminumlayer was placed under the films to make the materials absorb a greaterportion of the incident laser beam and the stream of high pressureassist gas used in many laser cutting processes was leveraged to providea clamping force between the films while the laser energy is delivered.This particular application included parts larger than the bed of theCNC laser available so a reel-to-reel fixture was implemented that fitwith the laser cutter such that continuous patterns up to 50′ long werecreated.

Another embodiment can comprise a piece of manufacturing equipment forlaser welding and cutting of polymer films. This example machinedirectly receives 8′ long rolls of 2-ply films, and uses a 70 W CO₂laser carried on a 4′×8′ CNC gantry to weld the layers together in anappropriate pattern.

In some embodiments, because the laser beam spot size required forwelding is an order of magnitude greater than that needed for cutting, adedicated optics system can be implemented that welds at the laser beamfocus position and has low beam divergence which means that the positionof the laser beam focus relative to the material position in the out ofplane direction (z-axis), can be tolerant to positioning errors. Thiscan reduce the alignment and precision requirements of the CNC structurewhich has a percolating effect on the cost and complexity of themachine.

Also, because of the lower power needed for welding as opposed tocutting in some embodiments, such embodiments can utilize a lower-costair cooled laser that can be directly mounted to the CNC gantry asopposed to flying optic systems with a stationary laser source usuallyused in conventional laser cutters. Additionally, the reel-to-reelmaterial handling functionality required to process films sourced onlarge rolls can be built into the machine which enables an automatedsystem that can run precisely with minimum user interaction.

Such a system can also be configured to accept various pieces ofinspection equipment that can be beneficial for performanceapplications. A machine vision system and/or laser displacement sensor,can be used to verify the position and/or characteristics of theresulting weld.

Any suitable material can be welded using direct-laser welding. For heatexchanger applications, it can be desirable to select a material thatcan withstand relatively high operating temperatures and environmentalexposure while retaining its resistance to puncture and bulk failuremodes such as creep under hoop stress. The development of suitablematerial/process combinations in conjunction with a design that limitsthe stress induced within the resulting heat exchanger can give asolution that is low cost and high performance.

A wide variety of additives can be used to tune a material's specificperformance, in addition to various lamination, weaving, andmulti-material composite approaches that can be utilized to improve thebulk performance of a given film. Accordingly, although direct laserwelding using a CO₂ laser source can be desirable in some embodiments,alternate welding methods can be desirable in other embodiments.

As discussed above, transmissive laser welding, ultrasonic/RF welding,and the like, can provide advantages by virtue of the ability togenerate heat at the weld interface. This can allow for film compositeswith woven or thermoset functional layers and thin thermoplastic bondinglayers needed for welding. In various embodiments, transmissive laserwelding can use a fiber laser source with a wavelength of 1 um asopposed to the 10.6 um wavelength of a CO₂ laser source. Accordingly,further embodiments can include an ultrasonic/RF welder capable ofprocessing continuous materials in a reel-to-reel format.

Strength can be a desirable property for membrane heat exchangers 100,as a stronger material does not need to be as thick, leading to costsavings and slightly improved thermal transfer. In various embodiments,strong polymers are also the least flexible polymers, and while strengthis desired, so is flexibility. Flexibility can improve with thinmaterials, so in some embodiments, a strong but stiff polymer can bethin enough in one of these heat exchangers to be appropriatelyflexible. Materials selection can involve balancing the strength andflexibility of the material with the interrelated geometric constraints,including thickness, imposed by the heat exchanger design. In variousembodiments, it can be desirable to apply one or more resins to apolymer heat exchanger. Additionally, introduction of additives to apolymer and/or resin can improve lifetime, conductivity, andprocessability, and the like.

In one preferred embodiment, a heat exchanger can comprise polyethyleneterephthalate, (PET, Mylar). In another preferred embodiment, a heatexchanger can comprise high density polyethylene (HDPE), which can beformulated for long lifetimes outdoors. In one embodiment, HDPE can becross-linked to form PEX, which has improved creep properties over othermaterials but otherwise retains the strength and flex properties ofHDPE.

While various polymers can be quite robust, they can be substantiallyweakened by creep, and environmental exposure can further weaken orembrittle materials. UV and abrasive particle exposure are potentiallydetrimental to the heat exchanger, but such exposures can, at least inpart, be dealt with through design. For example, the entire device canpotentially be built in a light-proof enclosure.

Materials for use in a polymer heat exchanger can be further optimizedfor welding and/or to withstand the constant stress that a pressurizedheat exchanger can experience. Polymer creep can be minimized in someembodiments through appropriate resin selection, polymer cross-linkingafter welding, additional material structure such as reinforcing fibers,ribs, or supporting scaffolding, or the like.

Fouling can be minimized in some embodiments through the use of saltwater, chlorinated water, or another liquid. The chemical resistance ofmany polymers allows for a range of fluid and additive options. Thechemical resistance of some polymers can allow maintenance procedureswhere the fluid system is flushed to clean out any fouling that hasoccurred.

While fouling can suggest biological growth, precipitation, or corrosionoccurring at an interface with a liquid, it is also possible to haveair-borne material foul the surface on the air-side of the heatexchanger. Material deposition and sticking at the heat exchange surfacewith air is likely controlled by the surface chemistry of the polymer,something that can be controlled through both materials selection andprocessing. Additionally, as with the liquid-polymer interface, therobustness of the polymer will allow a number of cleaning options to beexplored if it is determined that fouling of the air-polymer surfacemeaningfully decreases performance.

Turning to FIG. 9, in various embodiments, a plurality of membrane heatexchangers 100 can be configured together into a cross-flow heatexchanger array 900, wherein the plurality of membrane heat exchangers100 are stacked in parallel with a space 905 separating each of themembrane heat exchangers 100. The heat exchanger array 900 can beconfigured to cool fluid that is passing through the chambers 110 of thestacked heat exchangers 100 by having cold air 901 enter a first end 906of the spaces 905 separating the heat exchangers 100 such that the coldair 901 passes over the chambers 110. The cold air 901 can receive heatenergy from fluid flowing within the chambers 110 of the heat exchangers100, which heats the cold air 601 as the cold air 601 travels throughthe spaces 905 separating the heat exchangers 100 such that hot air 902leaves from a second end 907 of the heat exchanger array 900.

Although this example illustrates air 901 being used to cool fluidpassing through the chambers 110 of the stacked heat exchangers 100, infurther embodiments, any suitable fluid can be used to heat or coolvarious suitable fluids passing through the chambers 110. In otherwords, a liquid or gas can flow through the chambers 110 of a heatexchanger array 900 and be heated or cooled in various embodiments.Additionally, a liquid or gas can flow through spaces 905 of a heatexchanger array 900 to heat or cool a fluid passing through the heatexchangers 100 in accordance with further embodiments.

In various embodiments, membrane heat exchangers 100 can be held intension via an external compressively loaded structure, providing for alight weight, structurally strong, heat exchanger array 900. In someembodiments, an external membrane element support structure can besubject to mass manufacture and this assembly process can, in manyembodiments, be automated. In some embodiments, membrane heat exchangerfilms can be reinforced with additional layers, enabling strongattachment points and strengthened fluid interconnections betweenadjacent membrane heat exchanger elements.

FIG. 10 illustrates a further embodiment 900B of a heat exchanger array900 that comprises a plurality of stacked membrane heat exchangers 100,which are supported within a housing 1005, that is coupled on respectiveends of the heat exchangers 100. The heat exchanger array 900 furthercomprises fluid conduits 1010, which extend through and communicate withports 650 that communicate with ends 111 of the heat exchangers 100 (seee.g., FIGS. 6a and 6b ). For example, a flowing fluid can be received ata first fluid conduit 1010, flow into the chambers 110 of the heatexchangers 100 via respective first ends 111 and then flow out secondends 111 into a second fluid conduit 1010.

In various embodiments, a plurality of heat exchanger arrays 900 can bearranged into a heat exchanger assembly. For example, FIGS. 11 and 12illustrate some examples of heat exchanger assemblies that comprise aplurality of heat exchanger arrays 900. FIG. 11 illustrates a firstembodiment of a heat exchanger assembly 1100 having a plurality of heatexchanger arrays 900 disposed in a separated and stacked configuration.In one embodiment, such a system 1100 can be used for desalination,which is discussed in more detail below. In another embodiment, such asystem 1100 can be a portion of a condenser where gas can be condensedand collected in a collection try, which in some embodiments can bepresent as a bottom tray portion of the housing 1005. FIG. 12illustrates an example of a heat exchanger system 1200 that comprises aplurality of heat exchanger arrays 900 and comprises a fan assembly1210. Further embodiments of heat exchanger systems comprising a fanassembly 1210 are illustrated in FIGS. 12-19 b

Fan Membrane Heat Exchanger Systems

The United States devotes 12% of total energy consumption to spaceheating and cooling. In various embodiments, a plurality of membraneheat exchangers disclosed herein can be implemented as a fan systemconfigured to cut building heating and cooling energy use. An example ofsuch fan systems are illustrated in FIGS. 12-19 b and are discussedbelow.

Advances in computer-controlled manufacturing and polymer processing asdisclosed herein enable the fabrication of membrane heat exchangers withdramatically lower material thicknesses and lower material density thanexisting metal versions, leading to higher surface areas for a givenmass and cost. By using sufficiently thin membranes, the performance ofa heat exchanger 100 for an air conditioner or heat pump becomes limitedby the surface area of the membrane, not by the thermal conductivity ofthe material. The large heat transfer area allows lower temperaturedifferentials across these heat exchangers, high volumetric flow rateswith low linear velocities, resulting in doubled effective Carnotperformance. Additionally, various embodiments of a fan membrane heatexchanger can be retrofitted into existing building stock.

In various embodiments, reducing the temperature differential acrossheat exchangers can improve effective Carnot performance by a factor of2 for cooling systems and by 2 or even 3 or more for heating systems.Membrane heat exchangers 100 can also pave the way for lower-cost andmore efficient outdoor heat exchangers, heat pump hot water heating, drypower plant cooling, liquefaction of gases (including natural gas),desalination, and the like.

Coefficient of performance for a heat pump is given by

$\begin{matrix}{{COP}_{coolin} = {{\frac{T_{c}}{\left( {T_{h} - T_{c}} \right)}\mspace{14mu}{COP}_{heating}} = \frac{T_{h}}{\left( {T_{h} - T_{c}} \right)}}} & (1)\end{matrix}$

where T_(h) and T_(c). are the hot and cold temperatures of the Carnotcycle.

The temperature difference ΔT across a heat exchanger directly equatesto a loss in exergy that reduces the overall coefficient of performance.This is shown by extending the Carnot coefficient of performanceequations to include heat exchanger temperature differentials.

$\begin{matrix}{{COP}_{cooling} = {{\frac{\left( {T_{c} - {\Delta\; T}} \right)}{\left( {T_{h} + {\Delta\; T}} \right) - \left( {T_{c} - {\Delta\; T}} \right)}\mspace{14mu}{COP}_{heating}} = \frac{\left( {T_{h} + {\Delta\; T}} \right)}{\left( {T_{h} + {\Delta\; T}} \right) - \left( {T_{c} - {\Delta\; T}} \right)}}} & (2)\end{matrix}$

However, ΔT is constrained by the need to exchange heat at a sufficientrate. With reference to FIG. 6a , this heat transfer is given by

$\begin{matrix}{Q = {{h_{1}A\;\Delta\; T_{1}\mspace{14mu} Q} = {{h_{2}A\;\Delta\; T_{2}\mspace{14mu} Q} = {\left. \frac{{kA}\;\Delta\; T_{3}}{t}\Rightarrow Q \right. = \frac{A\;\Delta\; T}{\frac{1}{h_{1}} + \frac{1}{h_{2}} + \frac{t}{k}}}}}} & (3)\end{matrix}$

where A is the surface area of the heat exchanger, t is the wallthickness, k is the thermal conductivity of the material, and h₁ and h₂are the heat transfer coefficients of either fluid, and Q is the heattransfer. Thus, we can decrease ΔT while keeping the heat flow, Q,constant by increasing the surface area, A, and lowering the thickness,t. Thin film polymer membranes of various embodiments can enable anincrease in surface area and heat exchanger performance. While polymershave lower thermal conductivities, k, than metals, their thickness canbe made small enough that t/k is small relative to 1/h₁ and 1/h₂.

It can be shown that for laminar flow in a constant heat flux tube, theheat transfer coefficient can be approximated by

$\begin{matrix}{{Nu} = {{\frac{48}{11}\mspace{14mu} h} = \frac{{Nu}\mspace{14mu} k_{fluid}}{d}}} & (4)\end{matrix}$

where Nu is the Nusselt number, k_(fluid) is the thermal conductivity ofthe fluid, d is the effective tube diameter. Heat transfer in thisregime is independent of fluid velocity. However, heat transfer is alsoconstrained by the available heat capacity in the fluid which is givenby

Q={dot over (m)}c _(p)(T ₂ −T ₁)   (5)

where {dot over (m)} is the mass flow rate, c_(p) is the fluid specificheat capacity, and T₁ and T₂ the entering and exiting fluidtemperatures. Hence counter flow heat exchangers are preferred in someembodiments and mass flow rates should ideally be high in suchembodiments, so as to minimize the required fluid temperature change.

It can be shown that for laminar flow, flow losses are approximated by

$\begin{matrix}{{Re} = {{\frac{\rho\;{vd}}{\mu}\mspace{14mu} F_{D}} = {{\frac{64}{Re}\mspace{14mu}\Delta\; p} = {\left. {F_{D}\frac{L}{d}\frac{\rho\; v^{2}}{2}}\Rightarrow P_{fan} \right. = \frac{8A\;\mu\; v^{2}}{d}}}}} & (6)\end{matrix}$

where Re is the Reynolds number, ρ the fluid density, v the fluid speed,μ is the fluid viscosity, F_(D) the tube flow friction factor, Δp thetube pressure drop, L the tube length, and P_(fan) is the required fanpower.

Hence for a given amount of heat transfer, fan power can be minimized insome embodiment by utilizing a low air flow speed, but high mass flowrate, necessitating a large heat exchanger cross-sectional flow area, asenabled through the use of polymer-membrane heat exchangers. Low airflow speeds infer low Reynolds numbers, hence the laminar flowassumption in this case.

As discussed above, in various embodiments, membrane heat exchangers cancomprise a plurality of thin-wall tubes instead of the conventionalheavy metal tubes with soldered on fins. By Equation 3, low thermalconductivity materials can be used in various embodiments of heatexchangers as long as the thickness is very low. Based on hoop stress,the wall thickness required to hold a given pressure is

t=(Pressure−Tube radius)/Material stress   (7)

A smaller tube radius means lighter and cheaper membranes with betterthermal conduction. Four times as many tubes of half the diameterdoubles heat transfer for the same system mass/cost. Membrane heatexchanger tube diameters in the 1-5 mm range are likely, with surfaceheat transfer coefficient h of around 50-100 W/(m²K) for air, and5,000-10,000 W/(m²K) for flowing water.

Polyethylene terephthalate films (PET, Mylar), can have strengths ashigh as 200 MPa and thermal conductivities k in the 0.15-0.4 W/(mK)range, depending on additives. From Equation 7, assuming a safe workingstress of 50 MPa, a tube diameter of 3 mm, and a wall thickness of 0.05mm (2 mil), an operating pressure of up to 1.7 MPa (240 psi) is possiblein some embodiments. Thus k/t=3,000-8,000 W/(m²K), far higher than theair-side surface heat transfer coefficient h, so by Equation 3 the poorthermal conductivity of a thin PET film is not a limiting factor forperformance. For comparison, plastic shopping bags and Mylar balloonshave a thickness near 0.01 mm (0.5 mil), and are noted for being robustand long lived. In some preferred embodiments, membrane heat exchangerscan employ heavier membranes, 0.05 mm (2 mil), comparable to thethickness of freezer bags, but can go much thicker in furtherembodiments.

A combined ceiling fan and membrane heat exchanger system using chilledor warmed water capable of transferring 2.5 kW of cooling or heating canhave around 10 m² of surface area, 5 ° C. of total temperaturedifferential between water and air, and a plastic film mass of less than1 kg. The cost of bulk PET film is around $2/kg. The fan power requiredwould be a few watts, as would the required water pumping power, withflow speeds being low. The water mass flow rate would be around 0.25kg/s and the total mass of water in the heat exchanger would be around30 kg, assuming 3 mm diameter tubes. It is expected that these systemswill be retrofittable.

FIG. 12 illustrates an example embodiment of a heat exchanger assembly1200 having a plurality of heat exchanger arrays 900 that are disposedsurrounding and facing a fan assembly 1210 that includes a plurality ofblades 1211 that rotate on a shaft 1212 about an axis Z. The heatexchanger arrays 900 are disposed vertically parallel to axis Z andhorizontally tangential to axis Z to define a flow cavity 1205.

In such an embodiment, the fan assembly 1210 can be configured to movefluid through the heat exchanger arrays 900. For example, in oneembodiment, the fan assembly 1210 can be configured to suck fluidthrough the heat exchanger arrays 900 and into the flow cavity 1205. Ina further embodiment, the fan assembly 1210 can be configured to pushfluid from the flow cavity 1205 through the heat exchanger arrays 900.

FIG. 13 illustrates another example of a heat exchanger assembly 1300that comprises a plurality of membrane heat exchangers 100 disposed incylindrical configuration about a fan assembly 1210 to define a flowcavity 1205. The membrane heat exchangers 100 are generally arrangedwith the planar membrane heat exchangers 100 disposed in a plane facingand coincident with axis Z. The membrane heat exchangers 100 can becoupled via fluid conduits 1010 that are configured to provide for fluidflow through the membrane heat exchangers 100 as discussed herein.

FIG. 14 illustrates a further example of a heat exchanger assembly 1400that comprises a plurality of stacked membrane heat exchangers 100disposed about a fan assembly 1210 to define a flow cavity 1205. In thisexample embodiment, the membrane heat exchangers 100 can be octagonal inshape and stacked perpendicular to axis Z with spaces between the heatexchangers 100 configured to provide for fluid flow in and/or out of theflow cavity 1205. The heat exchangers 100 can be coupled together anddisposed on a plurality of rods 1410 that extend through the pluralityof heat exchangers 100. FIG. 15 illustrates a bottom view of the heatexchanger assembly 1400.

Although FIGS. 14 and 15 illustrate membrane heat exchangers 100 havinga polygon shape, further embodiments can have any other suitable regularor irregular shape. For example, FIG. 16 illustrates a furtherembodiment of a membrane heat exchanger 1600 that can form a portion ofa heat exchanger assembly, or the like. In this example, the membraneheat exchanger 1600 can be generally C-shaped having an open side 1065and defining a flow cavity 1205.

FIG. 17 illustrates a further embodiment of a membrane heat exchanger1700 that comprises a circular housing 1710 that surrounds a fanassembly 1210 and defines a flow cavity 1205. A plurality of stacked andspaced apart membrane heat exchangers 100 are disposed in a planeparallel to axis Z such that the fan assembly 1210 can push or pullfluid through the membrane heat exchangers 100. In various embodiments,the housing 1710 can be disposed on a plurality of legs.

As discussed herein, membrane heat exchanger arrays and assemblies canact as a heat exchanger in various suitable ways and FIGS. 18 a, 18 b,19 a, 19 b and 20 illustrate various embodiments of membrane heatexchanger systems. For example, FIG. 18 illustrates an example of amembrane heat exchanger system 1800 that includes one or more membraneheat exchangers 100 extending perpendicularly to axis Z of a fanassembly 1210. Hot water can enter the one or more membrane heatexchangers 100 at a first end 111A and be cooled as it flows through theone or more membrane heat exchangers 100 to a second end 111B, wherecold water emerges.

As shown in this example, the fan assembly 1210 pulls cold air fromunder the one or more membrane heat exchangers 100, past the one or moremembrane heat exchangers 100, and into a flow cavity 1205 defined by ahousing 1805. The cold air receives heat from the hot water flowingthrough the one or more membrane heat exchangers 100 such that hot airenters, flows through, and is expelled from the flow cavity 1205. Insome embodiments, the membrane heat exchanger 1700 of FIG. 17 canoperate in an analogous way.

FIG. 18 illustrates a further embodiment of a membrane heat exchangersystem 1801 that includes one or more membrane heat exchangers 100extending parallel to axis Z of a fan assembly 1210. Hot water can enterthe one or more membrane heat exchangers 100 at a first end 111A and becooled as it flows through the one or more membrane heat exchangers 100to a second end 111B, where cold water emerges.

As shown in this example, the fan assembly 1210 pulls cold air that isexternal to the flow cavity 1205 past the one or more membrane heatexchangers 100, and into the flow cavity 1205 defined by a housing 1805.The cold air receives heat from the hot water flowing through the one ormore membrane heat exchangers 100 such that hot air enters, flowsthrough, and is expelled from the flow cavity 1205. In some embodiments,the membrane heat exchangers 1200, 1300 of FIGS. 12 and 13 can operatein an analogous way.

In some embodiments, it can be desirable to operate a membrane heatexchanger at below atmospheric pressure. There are multiple ways ofaccomplishing this with the membrane heat exchanger 100, includingsituating the entire heat exchanger 100 within an evacuated chamber,which could be made of concrete, steel, composites, or any suitabletensegrity-type construction, and inverting the membrane heat exchangersuch that atmospheric air pressure flows through the tubes while watercondenses on the outside of the tubes. In various embodiments, it can bedesirable for the heat exchanger assembly to be externally tensioned soas to offset the partially evacuated condenser volumes of theinterstices between tubes.

For example, as illustrated in FIGS. 19a and 19b one example system 1900includes a condenser 1910 for a steam turbine 1920 (or desalinationplant), where hot water from the condenser 1910 enters a first end ofthe heat exchanger system 1800 at a first end 111A via a first supplyline 1905. The hot water is cooled by the heat exchanger system 1800 andexits via the second end 111B via a second supply line that returns tothe condenser 1910 directly as shown in FIG. 19a or via a reservoir 1925as shown in FIG. 19 b.

In addition to fluid conditioning with a system that comprises a fanassembly as illustrated in FIG. 12-19 b, in some embodiments, a heatexchanger wall system 2000 as illustrated in FIG. 20 can be configuredfor cooling fluids in an internal space. For example, as illustrated inFIG. 20, an external and internal heat exchanger 100A, 100B can bedisposed on opposing sides of a wall 2020, and a heat exchanger 2010disposed within the wall can be configured to move fluids within theheat exchangers 100 to cool internal fluid (e.g., air) associated withthe internal heat exchanger 100B and expel heat into the externalenvironment via the external heat exchanger 100A. However, in furtherembodiments, such a system can be used to heat internal fluid (e.g.,air) associated with the internal heat exchanger.

Desalination Via Membrane Heat Exchangers

FIGS. 11 and 21 illustrate two example heat exchanger embodiments 1100,2100 that can be deployed in a desalination system together into across-flow heat exchanger. Desalination methods performed can includeone or more of multi-stage flash (MSF), multiple effect desalination(MED), mechanical vapor compression (MVC), and the like.

For example, FIG. 22 illustrates an example embodiment of a mechanicalvapor compression desalination system 2200. The desalination system 2200comprises a vacuum shell 2205 that surrounds and encloses a desalinationassembly 2210 under negative pressure. The desalination assembly 2210comprises one or more membrane heat exchanger 100 that define a centralfreshwater cavity 2215 and a salt water cavity 2220 external to ansurrounding the one or more membrane heat exchanger 100.

The desalination system 2200 can be configured to desalinate salt water2227 that enters the vacuum shell 2205 via an inlet pipe 2225 and issprayed onto an outer surface 2221 of the one or more membrane heatexchangers 100 facing the salt water cavity 2220. Desalinated waterevaporant 2222 is generated by the outer surface 2221 of the one or moremembrane heat exchanger 100, which can pass into the freshwater cavity2215, where the desalinated water evaporant 2222 condenses on aninternal face 2216 of the one or more membrane heat exchanger 100 withinthe freshwater cavity 2215 to generate desalinated liquid water 2217.

The desalinated liquid water 2217 moves to a freshwater reservoir 2218at the bottom of the freshwater cavity 2215, which can leave the vacuumshell 2205 via a freshwater exit port 2230. A fan assembly 2110 can bedisposed over the freshwater cavity 2215 to facilitate movement ofevaporant 2222 and/or condensation of the same by increasing thepressure of the evaporant 2222. On the other hand, concentrated brine2223 can pool in a brine reservoir 2224 at the bottom of the saltwatercavity 2220 and can be removed by brine exit ports 2235. Accordingly,the desalination system 2200 can be configured to mechanically compresswater vapor 2222 so that the vapor 2222 can condense at a slightlyhigher temperature and/or pressure than it evaporates at—on the backside2216 of the evaporating heat exchanger 100. The temperature differentialbeing equal to the boiling point elevation temperature plus the heatexchanger temperature drop.

In various embodiments, such a mechanical vapor compression desalinationsystem 2200 can operate on a single stage, if desired, and at ambienttemperature, avoiding the need for extensive heat recovery heatexchangers. This can also allows for the efficient use of low recoveryrates, where only a small proportion of water is recovered such that thesalinity of the brine solution 2223 is only slightly elevated. This canreduce the energy required to desalinate water, as the higher thesalinity becomes, the more energy is required to desalinate it. Also,this can avoid the production of a highly concentrated brine solution2223 that may be problematic to release back into the environment.

In some embodiments, a vacuum or negative pressure can be generatedwithin the vacuum shell 2205 in various suitable ways including via anair pump or via pumped water flow within the sealed system. In otherwords, in some embodiments, desalination system 2200 can operate withoutan air pump, which can be desirable for reducing energy costs.

FIG. 23 illustrates an example embodiment of a multi-stage thermaldesalination system 2300 that comprises a pressure vessel body 2305 thatdefines a plurality of pressure chambers 2310 arranged in series witheach stage at a slightly lower pressure and temperature than theprevious stage. Each pressure chamber 2310 can comprise one or moremembrane heat exchanger configured to desalinate seawater thatintroduced via seawater pipe 2315, with the result being colderconcentrated brine and fresh water leaving the system 2300 viarespective brine and water outlets 2320, 2325. For such multiple effectdesalination systems 2300 any suitable number of stages or pressurechambers 2310 can be used, including two stages, five stages, twentyfour stages, a hundred stages, or other suitable number.

Many forms of membrane heat exchangers 100 can be used with the exampledesalination systems 2200, 2300 discussed above. For example, a membraneheat exchanger 100 can comprise a plurality of small tubes of largecollective surface area that separate two fluids of slightly differenttemperatures. In some embodiments, the smaller the difference intemperature between the fluids, the lower the energy loss and the moreefficient the heat exchanger system can be. As discussed herein,membrane heat exchangers 100 can be constructed by welding two thinfilms together so as to form a network of small chambers 110.

Isothermal Compressor

Conventional air compressors tend to use adiabatic compression where airwarms up during compression, increasing the work required. Often inmultistage compressors, intercooler heat exchangers are used to cool theair down again prior to further compression, thereby reducing the amountof work required. Isothermal compression can be more efficient thanadiabatic compression by producing a high pressure gas supply at ambienttemperature.

In some embodiments, by squashing a large surface area membrane heatexchanger 100 having small diameter gas-filled tubes with a pressurizedambient-temperature liquid it can be possible to combine a compressorand membrane heat exchanger 100 so as to achieve lower power isothermalcompression. Operating as an air motor, various embodiments of anisothermal compressor or motor system can absorb heat from theenvironment so as to reheat the expanding gas and increase the poweroutput from a compressed gas source. Such an isothermal compressor/motorcan be used to construct a Carnot cycle heat engine or heat pump invarious embodiments as discussed in further detail herein.

FIG. 24 illustrates an example embodiment of isothermal compressor 2400that comprises a cylinder 2405 which defines a compression cavity 2410.A membrane heat exchanger 100 can be disposed within the compressioncavity 2410 with an inlet/outlet port 2430 of the membrane heatexchanger 100 extending through the cylinder 2405. In this example, apiston 2415 can be configured to translate within the cylinder 2405 toincrease and decrease the volume of the compression cavity 2410. Thepiston 2415 can be driven by a con rod 2420 that is coupled to arotating crank 2425.

In various embodiments, the membrane heat exchanger 100 can comprise acompressible bladder which can include one or more chamber 110 withrespective ends 111 that communicate with respective inlet/outletportions of the port 2430. In some embodiments, the membrane heatexchanger 100 can be compressed by the piston or other suitablemechanism, either directly or indirectly. For example, in someembodiments, the compression cavity 2410 can be filled with a liquidsuch as water, oil, or the like, which can serve to compress themembrane heat exchanger 100 disposed within the compression cavity 2410.

The isothermal compressor 2400 can operate by having a compressiblefluid such as a gas introduced to membrane heat exchanger 100 while in anon-compressed configuration. The membrane heat exchanger 100 can becompressed, which can compress the fluid within the membrane heatexchanger 100. For example, chambers 110 that comprise fluid such as agas can be squashed flat when the membrane heat exchanger 100 iscompressed as illustrated in FIGS. 25a-c respectively.

Such compression can generate heat in the gas and such heat can betransferred through the body 105 of the membrane heat exchanger 100 fromthe gas to the liquid within the compression cavity 2410, such that thegas remains at near the same temperature as the fluid within thecompression cavity 2410, thereby achieving near isothermal compression.In various embodiments, it can be desirable to have a high surface areaof the chambers 110 of the membrane heat exchanger 100 to improve heattransfer between the compressed gas within the chambers 110 and thefluid within the compression cavity 2410.

The membrane heat exchanger 100 can be configured in various suitableways to facilitate compression of fluid within one or more chamber 110.For example, in some embodiments, any of the planar and rectangularmembrane heat exchangers 100 (e.g., as illustrated in FIGS. 1a-6b ) canbe configured in a foldable configuration that supports compression ofthe one or more chambers 110 and the flow of fluid therethrough. FIG. 26illustrates a further embodiment of a compressible membrane heatexchanger 100, which is illustrated having a coiled planar body thatdefines a chamber 110 that extends between a first and second end 111.The coiled body 105 can define a central orifice 1610 in variousembodiments. Accordingly, in such embodiments, compression of fluidwithin the chamber 110 can be achieved via physical compression betweenadjoining stacked portions of the body 105 and/or compression generatedby a fluid that surrounds such a membrane heat exchanger 100 within thecompression cavity 2410.

In further embodiments, compression of a membrane heat exchanger 100 canbe achieved without a piston 2425 or other direct action. For example,FIG. 27 illustrates an isothermal compressor 2400 that comprises a tankbody 2705 defining a compression chamber 2710 into which a fluid (e.g.oil, water, or the like) can be pumped to compress a membrane heatexchanger 100 disposed within the compression chamber 2710. In thisexample embodiment, the membrane heat exchanger 100 can comprise aseries of double diaphragm membranes 2735 within which a compressiblefluid (e.g., a gas such as air or the like) can be isothermallycompressed/expanded in response to the hydraulic action generated byfluid being introduced to and/or removed from the compression chamber2710 via an actuation port 2740. The double diaphragms 2735 canexpand/flatten in response to hydraulic action to compress gas withinthe chambers 110 of the membrane heat exchanger 100.

In some embodiments, a thin compliant membrane heat exchanger 100 cancomprise non-polymeric materials including but not limited to ceramics,metals, and the like. Such materials may be desirable for providingoperation at relatively high temperatures. For example, in oneembodiment, the membrane heat exchanger 100 can comprise a thin metallicmembrane element that can operate at high temperatures and with lowhysteresis losses. A metallic bellows can be used in such an embodiment,which can have many large diameter mostly flat convolutions with smallinternal air gaps and a small inner convolution diameter such that theheat transfer surface area to volume ratio can be high, and nearisothermal compression and expansion can thereby be achieved.

For low-temperature compressors, heat pumps, engines, or the like,plastic and composite construction beyond that of the heat exchangermembranes 100 can be used. For example, variable volume bellowsstructures (or equivalent), connecting rods, and crank cases can be madefrom low cost and light weight plastic and composite parts. In someimplementations, metallic bellows can have the advantage of lowerhysteresis losses than plastics or composite materials and therebyprovide higher efficiency.

In some embodiments, the fluid in the heat exchanger can be limited to afairly incompressible fluid. For example, in the case of an airconditioning system, a further water loop can be used to move heat toand from the vapor compression cycle and to transfer that heat to theair via the membrane heat exchanger. This can mitigate most of theefficiency advantage compared to a direct to air, air conditioningsystem. In one embodiment, the near isothermal compression and/orexpansion membrane can be directly mechanically compressed without theaid of a hydraulic fluid. External heat transfer can be achieved viadirect radiation, for example, solar, through a near constant pressuregas flow, or the like.

Applications of isothermal compressors and motors can include, but arenot limited to, air compression, natural gas compression, gascompression, gas liquefaction, hot water heating, liquid heating, liquidcooling, compressed air motors, and so forth. Further applications ofheat pumps using near-isothermal compression/expansion can include, butare not limited to, air conditioning, space heating, water heating,cooking, refrigeration, liquefaction, cryo-cooling, and so forth. Stillfurther applications of isothermal engines can include, but are notlimited to, waste heat recovery, solar hot water engines, geothermalengines, external combustion engines including those driven by wasteincineration, bottoming cycles, ocean thermal gradient engines, and soforth.

Various embodiments can be configured to provide 30% more efficientsmall and large scale compression of air and gases, and energy recoveryfrom pressurized gases. Further embodiments can be configured to providemore efficient single stage large and small scale hot water heaters andcryogenic coolers, with specific application to liquefied natural gas.

In some embodiments, the combined hydraulic and heat transfer fluid canbe directly coupled to an external heat exchanger. In some embodiments,the combined hydraulic and heat transfer fluid can be effectively pumpedthrough the isothermal compressor/expander by the isothermalcompression/expansion pumping process. In some embodiments, isothermalcompression/expansion can be driven via direct mechanical contact andthe external heat transfer fluid is maintained at relatively constantpressure largely independent of gas compression/expansion pressure. Insome embodiments, external heat transfer can be achieved by acondensing, evaporating, radiating, or forced convection heat transferprocess. In some embodiments the internal thermodynamic process caninclude compression, expansion, condensing and evaporation.

In some embodiments, mechanically actuated hermetically sealed compliantvolumes are used to compress and expand the hydraulic heat transferfluid (e.g., bellows, roll socks, and such like—this can avoid the needfor piston seals and the friction and leakage there entailed). At hightemperatures thin metallic sheets can be used in some embodimentsinstead of polymer films, these might also be construed into very highsurface area bellows geometries that minimize internal dead volume andallow direct mechanical as opposed to hydraulic actuation. Isothermalcompression/expansion at cryogenic temperatures, is also contemplated infurther embodiments, which can use Teflon films, and other cryogenicallycompatible polymers and composites, it can also use thin metallic sheetsin large double diaphragm forms.

Isothermal compression/expansion systems described herein can be usedfor gas compression, gas expansion, heat engines, heat pumps,liquefaction of gases, and the like. Gas liquefaction can begin byisothermal compression to high pressure at ambient temperature. Thesecond thermodynamic process can be adiabatic expansion to cryogenictemperatures. The third process can be isothermal expansion at theboiling point of the fluid, condensing it. Gas not condensed can bereturned to the ambient temperature isothermal compressor via a counterflow heat exchanger where it cools gas from the ambient temperatureisothermal compressor to cryogenic temperatures. Alternatively, a systemof heat pump and heat exchangers might be used to liquefy a gasdirectly. Relevant heat pumps and heat engines can comprise any suitablethermodynamic cycle based on isothermal compression and/or expansion.This can include Carnot cycles, Stirling cycles, Ericsson cycle, and soforth.

Combining this isothermal compression and expansion process with acounter flow heat exchanger or an adiabatic compression and expansionprocess, it is possible to make a highly efficient Carnot equivalentheat pump or heat engine.

Near Carnot Isothermal Engine and/or Heat Pump

Top conventional engines are limited to around 70% of Carnot, and onlyachieve these efficiencies at large scale and at ideal temperatures.Most engine types typically operate at far lower efficiency than this.Small scale distributed energy engine solutions are therefore lacking.

However, in accordance with various embodiments, by hydraulicallysquashing large surface area gas-filled membrane heat exchangers 100, itcan be possible to combine a compressor and heat exchanger so as toachieve near isothermal compression or expansion. In some embodiments,the membrane heat exchanger body 105 separating the liquid from the gasmay only serve as a fluid-to-gas barrier and may not otherwise besignificantly loaded. As discussed herein, a membrane heat exchanger 100can be thin and compliant; thin enough that in some embodiments, lowconductivity polymers can be used without compromising overall heattransfer. At higher temperatures, metallic foils can be used in someembodiments. Suitable hydraulic cooling/heating fluids can includewater, liquefied gases, heat transfer oils, molten salts, molten metals,and the like.

Accordingly, in various embodiments, with effective isothermalcompression and expansion it is possible to construct Carnot cycleengines and heat pumps of high efficiency including 80% of Carnot ormore. In some embodiments, operating a highly pressurized closed cyclesystem also enables high power densities. In further embodiments, a highsurface area bellows can be compressed directly and use alternate heattransfer without hydraulics.

In accordance with one example embodiment, and as shown in FIG. 28, anisothermal engine 2800 can comprise a first and second bellows 2805 thatdefine a respective compression chamber 2810 having a membrane heatexchanger 100 disposed therein. The bellows 2805 can be compressible,and in some embodiments such compression can be driven by a respectivecon rod 2420 that is coupled to a rotating crank 2425. For example, insome embodiments such as is illustrated in FIG. 28, the crank 2425 andcon rods 2420 can be in an alpha configuration with the crank being 90°out of phase.

In the example of FIG. 28, the bellows 2805 can be configured to holdfluids (e.g., water, oil, or the like) within the compression chambers2810 and the temperatures of the fluids can be different. For example,in one embodiment, the first bellows 2805H can be configured to hold hotfluid within the compression chamber 2810 and the second bellows 2805Ccan be configured to hold cold fluid within the bellows, with entry andexit of such hot or cold fluid from the compression chambers 2810 beingprovided by respective inlet and outlet ports 2811, 2812.

As discussed herein, the membrane heat exchanger 100 can define achamber 110 that extends between one or more end 111. In the example ofFIG. 28 an end 111 of the membrane heat exchangers 100 can be coupledwith a regenerator or counter-flow heat exchanger 2830 via a line 2820that extends through the counter-flow heat exchanger 2830. In someembodiments, the counter-flow heat exchanger 2830 can comprise amembrane heat exchanger 100 as discussed herein.

In various embodiments a membrane heat exchanger 100 can be disposedwithin a fluid-filled bellows 2805. As the bellows 2805, or equivalent,compresses, these membrane heat exchangers 100 can be hydraulicallysquashed together, compressing a gas disposed within the respectivechambers 110 of the membrane heat exchangers 100. Due to the highsurface area and small gas gap of various embodiments, heat can betransferred through the membrane from the gas to the liquid, such thatthe gas remains at near the same temperature as the fluid, therebyachieving near isothermal compression.

In other words, FIG. 28 depicts an isothermal engine or heat pump 2800(e.g., an Ericsson cycle) that incorporates isothermal compression andisothermal expansion, which can be connected by a regenerator 2820. Invarious embodiments, where an isothermal engine is backwards (e.g., theelectrical generator is powered as a motor to drive it) such anisothermal engine can be used as a heat pump.

Combining this isothermal compression and expansion process with acounter-flow heat exchanger 2830, various embodiments provide a highlyefficient Carnot equivalent heat pump or heat engine. The heat transfercan be highly efficient, friction and sealing losses can be very low,and the thermodynamic cycle near ideal. Many cycles and even-valvedapproaches are contemplated in some embodiments. In some embodiments,fatigue life of the membrane may be of concern, but can be mitigated byuse of very small deflections.

Accordingly, in some embodiments, low cost engines and heat pumps withefficiencies in excess of 80% of Carnot can be configured. For example,one embodiment can have 15% efficient engines with water at near boilingpoint, 40% efficient engines using heat transfer oils at 350° C., and50% with molten salts at 570° C. Accordingly, efficient and costeffective low temperature engines, bottoming cycles, and recovery ofwaste heat, at small and large scale, can be enabled.

In further embodiments, various other suitable configurations of anisothermal engine 2800 can be provided. For example, FIG. 29 illustratesan example embodiment 2800B of an isothermal engine 2800 having thebellows 2805 disposed in a parallel arrangement instead of in a 90°arrangement as in FIG. 28. Additionally, the bellows 2805 are shownbeing actuated by a driving assembly 2950. This example illustrates andisothermal engine or heat pump that uses flexures and linearmotors/generators so as to avoid the need for rotary motion (e.g., asillustrated in FIG. 28).

Additionally, in another embodiment 2800C, as illustrated in FIG. 30,bellows 2805 can be disposed within a respective cavity 3005 of ahousing 3001. In some embodiments, the cavities 3005 can be filled witha fluid (e.g., water) to surround the bellows 2805 to provide forcooling/heating of the respective bellows 2805, which can cool/heat afluid within the bellows 2805. In some embodiments, the cavities 3005can comprise open containers and the system 2800C can be disposedinverted compared to how it is shown in FIG. 30. As illustrated in thisexample, the compressible membrane heat exchangers 100 can be driven viaa crank 2425 coupled to a dual-arm con rod 2420. In various embodiments,high surface area bellows 2805 can be used for direct near isothermalcompression/expansion.

Additionally, as discussed herein, the term “isothermal” can refer tosystems or methods, or portions thereof, that operate in or atnear-isothermal or substantially-isothermal conditions. Accordingly, thepresent disclosure should not be construed to be limited to suchsystems, methods, or portions thereof that lack any temperature changewhatsoever.

Also, the terms “compression chamber” or “compression cavity” should insome embodiments be construed to include a structure that is configuredfor isothermal compression and/or expansion. For example, in variousembodiments, an isothermal engine can comprise an isothermal compressionchamber (cold) and an isothermal expansion chamber (hot). Thecompression and expansion chambers can be reversed in some embodimentswhen in a heat pump mode. Accordingly, the term “compression chamber”should not be construed to be limiting and can encompass an isothermalcompression chamber and/or an isothermal expansion chamber in accordancewith various embodiments.

Membrane Heat Exchangers Used in Spacecraft, Satellites and PlanetaryHabitats

Membrane heat exchangers 100 and related systems can be configured foruse with manned and unmanned spacecraft, satellites, and planetaryhabitats that need to be temperature regulated to sustain life oroperation of devices. Moving heat between components (via convection) ordissipating heat to space (via radiation) can involve embodiments ofmembrane heat exchangers 100 having a large area.

In various embodiments, Micro-Meteor and Orbital Debris (MMOD) can be adanger for membrane heat exchangers 100 and associated radiatorsoperating in and near space. Accordingly, in various embodiments, amembrane heat exchanger 100 can be configured to be resistant to,withstand or otherwise handle an operating environment having MMOD. Forexample, in some embodiments, a heat radiator can be designed to besacrificial and redundant or replacement radiators can be coupled to amembrane heat exchanger 100. Additionally, fluid paths within suchradiators can be made to be independent so that the effects of damage tothe radiator are isolated to the extent possible.

Further embodiments can include MMOD shielding that permits heattransfer. One example is shielding that is transparent to infraredradiation. Another example, as illustrated in FIG. 31 is an array 3105of elongated shielding channels 3110 are normal to the surface of aradiator or membrane heat exchanger 100 and are reflective, effectivelyacting as a short distance light-pipe for passing radiation to space.

In some embodiments such an array 3015 can comprise a Mylar orfiber-reinforced Mylar honeycomb-like shield structure in which thehoneycomb channels 3110 are normal to the radiator surface and arereflective. Impact energy from MMOD would be dispersed by the honeycombwalls 3115. In this scenario, the likelihood of an MMOD impact normal tothe honeycomb structure walls 3115, and the protection as a function ofimpact angle, can be considered. For example, short light-pipes of thistype do not need to contain line-of-sight to the emissive radiator wall,and could be made to be non-parallel so as to better prevent damage fromMMOD parallel to the light pipe.

The low cost of membrane heat exchangers 100 can enable new incarnationsof thermal management systems for spacecraft. For example, inflatableradiative heat exchanger panels can be applied directly to the outersurfaces of spacecraft, where they can further add to the micrometeoroidprotection and thermal insulation of the spacecraft. By using selectiveemissivity coatings these can operate in direct normal sunlight, ifpoorly, and heat transfer fluids can be controlled independently topanels that are in sunlight or shade so as to provide continuous overallcooling without use of active positioning of independent radiators. Thefar lighter weight of the inflatable radiators enables their use in thismanner where not all radiators are maximally effective at all times.Membrane heat exchangers 100 can further enable lightweightfluid-to-liquid heat exchangers of large effective area and efficiencysuch that the cost of operating secondary heat transfer loops, which canadd significant safety and redundancy, is far less prohibitive.

The described embodiments are susceptible to various modifications andalternative forms, and specific examples thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the described embodiments are not to belimited to the particular forms or methods disclosed, but to thecontrary, the present disclosure is to cover all modifications,equivalents, and alternatives.

What is claimed is:
 1. An air thermal conditioning system for at leastone of heating air and cooling air, the air thermal conditioning systemcomprising: a cross-flow heat exchanger array that includes: a housing;a plurality of at least 50 stacked planar membrane heat exchangersdisposed in parallel and held in tension by the housing via respectiveopposing top and bottom ends of the respective planar membrane heatexchangers, the planar membrane heat exchangers stacked in parallel witha space separating each of the planar membrane heat exchangers, witheach of the planar membrane heat exchangers comprising: a first planarpolymer sheet having a thickness between 0.1 mm and 0.05 mm; a secondplanar polymer sheet having a thickness between 0.1 mm and 0.05 mm, thesecond planar polymer sheet coupled to the first planar polymer sheet atleast by a welded seam; and at least one fluid chamber defined by thefirst and second planar polymer sheets and the welded seam, with the atleast one fluid chamber extending between the first and second ends andopening to a first and second port defined by the first and secondplanar polymer sheets at the top and bottom ends respectively; and afirst and second fluid conduit respectively disposed at andcommunicating with the first and second ports of the planar membraneheat exchangers, the first and second fluid conduits fluidicallycoupling the plurality of planar membrane heat exchangers and configuredgenerate a fluid flow within the fluid chambers of the plurality ofplanar membrane heat exchangers, the fluid flow: flowing into the firstfluid conduit, flowing between the top and bottom ends within therespective chambers, and flowing out the second fluid conduit, withfluid flowing in and out of the first and second fluid conduitsrespectively on the same side of the cross-flow heat exchanger array. 2.The air thermal conditioning system of claim 1, wherein the cross-flowheat exchanger array is configured to heat fluid that is passing throughthe fluid chambers of the stacked planar membrane heat exchangers byhaving hot air enter a first end of the spaces separating the planarmembrane heat exchangers such that the hot air passes over the fluidchambers, where the hot air transfers thermal energy to the fluidflowing within the fluid chambers of the planar membrane heatexchangers, which cools the hot air as the hot air travels through thespaces separating the planar membrane heat exchangers such that cold airis generated and leaves from a second end of the cross-flow heatexchanger array.
 3. The air thermal conditioning system of claim 1,wherein a fan is disposed proximate to the second end of the cross-flowheat exchanger array, and wherein the fan is configured to cause the hotair to be pulled into the first end of the spaces separating the planarmembrane heat exchangers such that the hot air passes over the fluidchambers of the planar membrane heat exchangers.
 4. The air thermalconditioning system of claim 1, wherein the fluid flow within the fluidchambers of the plurality of planar membrane heat exchangers comprises aliquid fluid flow.
 5. An air thermal conditioning system for at leastone of heating air and cooling air, the air thermal conditioning systemcomprising: a cross-flow heat exchanger array that includes: a housing;a plurality of planar membrane heat exchangers held by the housing inparallel via respective opposing first and second ends of the planarmembrane heat exchangers, the planar membrane heat exchangers disposedin parallel with a space separating each of the planar membrane heatexchangers, with each of the planar membrane heat exchangers comprising:a first sheet; a second sheet coupled to the first sheet; and at leastone fluid chamber defined by the first and second sheets, with the atleast one fluid chamber extending between the first and second ends andopening to a first and second port disposed at the first and second endsrespectively; and a first and second fluid conduit respectively disposedat and communicating with the first and second ports of the planarmembrane heat exchangers, the first and second fluid conduitsfluidically coupling the plurality of planar membrane heat exchangersand configured generate a fluid flow within the fluid chambers of theplurality of planar membrane heat exchangers flowing in the first fluidconduit, between the first and second ends within the respectivechambers, and out the second fluid conduit, with fluid flowing in andout of the first and second fluid conduits respectively on the same sideof the cross-flow heat exchanger array.
 6. The air thermal conditioningsystem of claim 5, wherein the plurality of planar membrane heatexchangers comprises at least 50 planar membrane heat exchangers.
 7. Theair thermal conditioning system of claim 5, wherein the plurality ofplanar membrane heat exchangers are disposed in parallel and held intension by the housing.
 8. The air thermal conditioning system of claim5, wherein the first and second sheets are planar polymer sheets havinga thickness between 0.1 mm and 0.05 mm.
 9. The air thermal conditioningsystem of claim 5, wherein the second sheet is coupled to the firstsheet at least by a welded seam, and wherein the first and second sheetsand the welded seam define the fluid chambers of the planar membraneheat exchangers.
 10. An air thermal conditioning system for at least oneof heating air and cooling air, the air thermal conditioning systemcomprising: a cross-flow heat exchanger array that includes: a pluralityof planar membrane heat exchangers disposed in parallel with a spaceseparating adjacent planar membrane heat exchangers, with each of theplanar membrane heat exchangers comprising: a first sheet; a secondsheet coupled to the first sheet; and at least one fluid chamber definedby the first and second sheets, with the at least one fluid chamberextending between first and second ends of the planar membrane heatexchangers and opening to a first and second port at the first andsecond ends respectively.
 11. The air thermal conditioning system ofclaim 10, further comprising a first and second fluid conduitrespectively disposed at and communicating with the first and secondports of the planar membrane heat exchangers.
 12. The air thermalconditioning system of claim 11, wherein the first and second fluidconduits couple the plurality of planar membrane heat exchangers and areconfigured support a fluid flow within the fluid chambers of theplurality of planar membrane heat exchangers flowing in the first fluidconduit, between the first and second ends within the respectivechambers, and out the second fluid conduit.
 13. The air thermalconditioning system of claim 11, wherein the first and second fluidconduits are disposed on the same side of the cross-flow heat exchangerarray.
 14. The air thermal conditioning system of claim 10, wherein theplurality of planar membrane heat exchangers are held by a housing viarespective opposing first and second ends of the planar membrane heatexchangers.
 15. The air thermal conditioning system of claim 14, whereinthe plurality of planar membrane heat exchangers are disposed inparallel and held in tension by the housing.
 16. The air thermalconditioning system of claim 10, wherein the plurality of planarmembrane heat exchangers comprises at least 50 planar membrane heatexchangers.
 17. The air thermal conditioning system of claim 10, whereinthe first and second sheets are planar polymer sheets.
 18. The airthermal conditioning system of claim 10, wherein the second sheet iscoupled to the first sheet at least by a welded seam, and wherein thefirst and second sheets and welded seam define the fluid chambers of theplanar membrane heat exchangers.
 19. The air thermal conditioning systemof claim 10, wherein the cross-flow heat exchanger array is configuredto heat fluid that is passing through the fluid chambers of the planarmembrane heat exchangers by having hot air enter a first end of spacesseparating the planar membrane heat exchangers such that the hot airpasses over the fluid chambers, where the hot air transfers thermalenergy to the fluid flowing within the fluid chambers of the planarmembrane heat exchangers, which cools the hot air as the hot air travelsthrough the spaces separating the planar membrane heat exchangers suchthat cold air is generated and leaves from a second end of thecross-flow heat exchanger array.
 20. The air thermal conditioning systemof claim 10, wherein a fan is disposed proximate to a second end of thecross-flow heat exchanger array, and wherein the fan is configured tocause air to enter a first end of spaces separating the planar membraneheat exchangers such that the air passes over the fluid chambers of theplanar membrane heat exchangers.